DESCRIPTION (Applicant's abstract) The current application is aimed towards the career development of Russell DeBose-Boyd, Ph.D., Instructor of Molecular Genetics at UT Southwestern Medical Center in Dallas, TX. To prepare the candidate for a research career as an independent investigator, a career development plan is described in which a mentored program is undertaken, encompassing an advanced research experience focusing on a specific research project under the guidance of an appropriate mentor. During the later phases of the program, progressive development of the candidate into an independent investigator will be provided. Experiences gained from the study of lipid metabolism in animals will be applied to parasitic organisms in hopes of creating better treatments for infected patients in economically deprived communities of the United States and the Third World. Excess sterols accelerate degradation of HMG-CoA reductase (HMGCR), a major focal point in the regulation isoprenoid biosynthesis in animal cells. The proposed studies are designed to test the hypothesis that interactions between HMGCR and sterols induce conformational changes in the protein, resulting in enhanced degradation of the enzyme. To gain further insight into this process, three specific aims will be pursued: (Aim 1) in search of residues important for mediating sterol-regulation, the hydrophobic NH2-terminal domain of HMGCR will be mutagenized in a PCR-based strategy. A selection scheme will be developed to identify mutations that render HMGCR refractory to sterol regulation. (Aim 2) An assay will be developed to detect structural changes in HMGCR upon sterol treatment, employing HMGCR-specific antibodies and a panel of proteases to probe for sterol-induced conformational changes. (Aim 3) Parallels between sterol regulation of HMGCR and other sterol-responsive proteins will be explored. Although an important component of cellular membranes, over accumulation of cholesterol is toxic because of its insolubility. Excess cholesterol in the bloodstream can deposit in arteries, initiating atherosclerosis, which can lead to heart attacks. A thorough understanding of molecular mechanisms controlling HMGCR levels may provide insights into novel therapies to treat coronary heart disease.